Breakable safety valve for metal-made container

ABSTRACT

The present invention is concerned with a cleavage type safety valve installed on a metal vessel for affording the explosion-proof function. The safety valve is installed on a small-sized cell vessel which remains hermetically sealed during the normal operation but instantly releases the pressure in the inside of the vessel if, due to abnormalities, such as overcharging, the pressure is increased and reaches a prescribed value to prevent explosion or deformation of the cell vessel. The metal foil type safety valve by the cold pressure welding of the present invention cold welds the metal foil for sealing the air vent hole in the metal vessel. If the internal pressure in the vessel reaches the prescribed value, the metal foil is cleft to form an opening in the vessel to release the internal pressure.

FIELD OF THE INVENTION

This invention relates to a cleavage type safety valve provided in ametal vessel of, for example, a secondary cell. More specifically, thepresent invention relates to cleavage type safety valve—therefor; foropening the pressure generated in the vessel in an emergency, forpreventing deformation or the like of the vessel for or for preventingdestruction of equipment.

BACKGROUND OF THE INVENTION

A high-performance secondary cell, such as lithium ion cell, whichrecently has come into widespread use, is characterized by a small size,lightness in weight and a large capacity, Lithium ion cells are used inincreasing numbers in a portable equipment, such as a portable telephoneset or a note-type computer.

However, this type of the high-performance secondary cell has a highenergy density in the cell, While a combustible organic solvent isoccasionally used as an electrolytic solution, such that, in case of anemergency, such as during shorting or overcharging in the cell,combustible gases tend to be evolved or ignited in the cell vessel andraise the internal pressure in the cell thus producing a problem such asinadvertent leakage of the cell contents—therefor;

If the internal pressure in the vessel exceeds the compressive strength,the vessel is deformed excessively. If the limit of compression isexceeded, the vessel explodes.

If such accident occurs during use of the portable equipment, the useris endangered or the equipment is destroyed.

For avoiding this risk, a cleavage type safety valve which, if theinternal pressure in the vessel is increased beyond a prescribed value,part of the vessel is cleaved to form an opening to open the internalpressure.

The cleavage type safety vale, used up to now, is classified into amarking type safety valve and a metal foil type safety valve, asselected depending on usage and application.

The marking type safety valve is of such a structure in which a markerpunch having a tooth end with a wedge-shaped cross-section is driveninto a portion of a vessel for machining a cleavage groove to a circularor the like contour so that, if the internal pressure of the vessel isincreased to higher than a prescribed value, the thin-walled portion ofthe bottom of the cleavage groove is cleft to open the internalpressure.

The marker type safety valve has merits in facilitated machining and lowmanufacturing cost.

However, in driving the marker punch, cracks generated at the tooth endof the marker punch are left in the thin-walled portion after machining,such that, if the thin-walled portion is of a reduced wall thickness,cracks are formed extending through the thin-walled portion, thuspossibly producing leakage.

The cleavage pressure in the marker type safety valve is determined bythe pressure-receiving surface surrounded by the cleavage groove and theplate thickness of the thin-walled portion of the bottom of the cleavagegroove. Thus, if it is desired to reduce the pressure-receiving surfacefor installment in a small-sized vessel and nevertheless it is desiredto prevent the cleavage pressure from increasing, the plate thickness ofthe thin-walled portion needs to be decreased further. However, if theplate thickness of the thin-walled portion is further reduced, the ratioof rejection due to leakage is increased. Thus, difficulties are met inreducing the size of the marker type safety valve.

The metal foil type safety valve is of such a structure in which a metalfoil is attached for closing the air vent hole in the vessel forhermetic sealing, so that, if the internal pressure in the vesselexceeds a prescribed value in case of an emergency, the metal foilbecomes cleft to open the internal pressure.

In the conventional metal foil type safety valve, the metal foil isattached by a welding method. Since the lower limit value of the platethickness of the metal foil that can be attached by the welding methodis not more than one-half the lower limit value of the plate thicknessof the thin-walled portion of the bottom of the cleavage bottom in caseof the marking type cleavage cell, the metal foil type safety valve can,in this respect, be reduced more easily in size.

However, in attachment of the metal foil by the welding method, thereare encountered problems of through-holes proper to the weldingprocessing and technical difficulties in attachment and hermetic sealingby the welding method. In addition, equipment investment becomes costlythus presenting cost and quality problems.

DISCLOSURE OF THE INVENTION

The present invention has developed a metal foil type safety valve bythe cold welding method (referred to hereinafter as the present safetyvalve) in which a metal foil is attached by a cold pressure weldingmethod for stopping air vent holes in a vessel to provide a safetyvalve.

The cold pressure welding method is a machining method in which portionsof two metal components to be welded together are pressed and weldedtogether at ambient temperature in a cold welding metal mold.

The welding principle resides in inducing plastic deformation in theweld by pressure applied by the clad pressure welding metal mold,generating a new surface in both contact surfaces by friction betweentwo contact surfaces and continuous pressing and holding in this statefor inducing interatomic linkage for welding the two componentstogether.

Heretofore, in cold pressure welding a metal foil with a plate thicknessof not more than 0.3 mm, such as is used in a metal foil type safetyvalve, the metal foil tends to be cracked or fractured by the pressureapplied by the cold pressure welding to produce leakage.

The present inventors have conducted re-check of a number of operatingconditions in cold pressure welding, including tooth profile of the coldpressure welding metal molds, weld shape, surface treatment or heattreatment in meeting with material types of the metal foils or thevessel, pressing rate for cold pressure welding and holding time at thelower dead point, by a trial-and-error method, and succeeded inattaching a metal foil with a plate thickness up to 0.01 mm by the coldpressure molding method, so far thought not possible, and in applyingthe attaching technique to the metal foil type safety valve.

The present safety valve has been confirmed to have many advantages,such as higher air tightness and a lesser number of occurrences oftroubles in hermetic sealing, shortened machining time, and suppressionof the machining time to approximately one-fifth, as compared to thecase of the conventional metal foil type safety valve by the light beamwelding method, as well as facilitated realization of an optimumcleavage pressure and diminished fluctuations in the cleavage pressurein case of mass production, which are two of the crucial factors assafety valves.

In an embodiment, the present invention provides an improved cleavagetype safety valve for a metal vessel that comprises a piece of metalfoil connected to the vessel and over an air vent hole in the vessel bycold pressure welding the foil to the vessel. The cold pressure weldingof the outer periphery of the foil to the vessel results in an hermeticseal over the vent hole provided by the metal foil. Further, the coldpressure welding of the foil to the vessel creates a thin-walled portionof the foil disposed radially inwardly of the weld. The thin-walledportion provides a reliable cleavage point in the event the vesselbecomes over pressurized.

In an embodiment where the metal vessel has a plate thickness of about0.8 mm, the metal foil layer has a plate thickness prior to the coldpressure welding of about 0.03 mm. However, the plate thickness at thethin-walled portion of the foil layer (that is disposed radiallyinwardly from the outer periphery of the foil layer that is coldpressure welded to the vessel) has a plate thickness of substantiallyless than 0.03 mm.

In an embodiment, the ratio of the plate thickness of the metal foil tothe plate thickness of the vessel is about 3:80.

In an embodiment, the ratio of the plate thickness of the metal foil tothe diameter of the air vent hole disposed in the vessel is about 3:150.

In an embodiment, the vessel and metal foil are fabricated from A3003.

In an embodiment, the vessel has dimensions of 34 mm×6 mm×47 mm and aplate thickness of about 0.8 mm. The air vent hole has a diameter ofabout 1.5 mm and the plate thickness of the metal foil layer is about0.03 mm. However, at the thin-walled portion inside of foil which isdisposed inside of the outer periphery of the metal foil layer, which iscold pressure welded to the edge of the vessel which defines the airvent hole, the thickness of the metal foil layer is substantially lessthan 0.03 mm and can be as thin as 0.005 mm.

In an embodiment, the vessel further comprises a vessel body having anopen end which is enclosed by a lid that is welded to the vessel body.The lid includes the air vent hole. The lid having dimensions of about34 mm×6 mm. The lid also having a plate thickness of 0.8 mm and furtherbeing fabricated from A3003.

In an embodiment, the vessel can withstand an internal pressure of atleast 15 kg/cm².

In an embodiment, the vessel can withstand an external pressure of atleast 50 kg/cm².

In an embodiment, the present invention provides a method of forming acleavage type safety valve in a vessel which comprises the steps ofproviding a vessel body having an open end, providing a lid for thevessel body, forming an air vent hole in the lid, cold pressure weldingan outer periphery of a metal foil layer over the air vent hole tohermetically seal the air vent hole and to provide a thin-walled sectionof the foil inside of the outer periphery or the weld, and welding thelid to the vessel body.

Other objects and advantages of the present invention will becomeapparent from reading the following detailed description and appendedclaims, and upon reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view looking from a lid of a cell vessel.

FIG. 2 is a cross-sectional view looking from the lateral side of thecell vessel.

FIG. 3 is a side view of a metal foil prior to cold pressure welding.

FIG. 4 is a cross-sectional view of a lid.

FIG. 5 is a cross-sectional view of a lid, a metal foil and a metal moldfor cold pressure welding prior to cold pressure welding.

FIG. 6 is a cross-sectional view of a lid, a metal foil and a metal moldfor cold pressure welding during cold pressure welding.

FIG. 7 is a cross-sectional view of a marker type safety valve.

FIG. 8 is an enlarged cross-sectional view showing a thinwalled portionof a metal foil after cold pressure welding.

FIG. 9 is a cross-sectional view of a lid when the internal pressure inthe vessel is below a prescribed value.

FIG. 10 therefor the state in which the internal pressure in the vesselreaches a prescribed value and the dome of the metal foil is reversed.

FIG. 11 therefor the state in which the thin-walled portion has becomecleft directly after the metal foil dome.

EXPLANATION OF NUMERALS

1, . . . lid; 2, . . . metal foil; 3, . . . cell can; 4, air vent hole;5, thin-walled portion; 6, . . . upper punch; 7, . . . lower punch; 8, .. . electrode pull-out opening; 9, . . . weld; 10, . . .pressure-receiving portion of a marker type safety valve; 11, . . .dome; 12, . . . plate thickness of the thin-walled portion; 13, . . .cleft groove.

It should be understood that the drawings are not necessarily to scaleand that the embodiments are sometimes illustrated by graphic symbols,phantom lines, diagrammatic representations and fragmentary views. Incertain instances, details which are not necessary for an understandingof the present invention or which render other details difficult toperceive may have been omitted. It should be understood, of course, thatthe invention is not necessarily limited to the particular embodimentsillustrated herein.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The present invention will be explained with reference to a preferredembodiment thereof.

In the present embodiment, to an opening of a square tube shaped cellcan 3, formed of an A3003 aluminum alloy, is welded a lid 1 formed ofthe same material to produce a metal vessel for a lithium ion secondarycell. To this metal vessel is mounted the present safety valve designedto be cleft at an internal pressure of 18 kg/cm².

The cell vessel shown in FIG. 1 and 2 is made up of a cell can 3 ofA3003, with a plate thickness of 0.8 mm and an outer size of 34 mm×6mm×47 mm, and a lid 1 of A3003, with a plate thickness of 0.8 mm and anouter size equal to the inner size of an opening of 34 mm×6 mm of thecell can 3.

At a mid portion of the lid 1 is formed an electrode pull-out opening 8,and an air vent hole 4, which is 1.5 mm in diameter, is formed betweenthe electrode pull-out opening 8 and the longitudinal end face of thecan. The lid 1 and the cell can 3 are connected to each other by awelding method. Outside of this air vent hole 4, a metal foil 2 ofA3003, with the plate thickness of 0.03 mm, is cold pressure welded andhermitically sealed.

In FIGS. 1 to 12, the plate thicknesses of the lid 1, metal foil 2, weld9, thin walled portion and the cleft groove 13, and the diameter of theair vent hole 4 in FIG. 4, are exaggerated for illustration. Moreover,the contents of the cell, irrelevant to the illustration of the presentinvention, are omitted in FIG. 2.

FIG. 3 shows the metal foil 2.

This metal foil 2 is cold pressure welded for stopping the air vent hole4, 1.5 mm in diameter, formed in the lid 1, to provide a safety valve.

Moreover, the lid 1 is inserted into the opening of the cell can 3 andwelded by a light or laser beam welding method to complete ahermetically sealed vessel.

In the present embodiment, 100 vessel not charged with contents werefabricated for the purpose of testing air-tightness and cleavagepressure of the present safety valve and a hole for testing the cleavagewas bored in the bottom of the cell can 3.

The test on air-tightness was conducted by applying an air pressure of8.0 kg/cm² to the completed vessel for 15 seconds and by measuringchanges in the pressure by an air leakage tester for judging thepossible leakage. There were found no occurrences of air leakage.

The cleavage pressure test was conducted on samples already tested forair-tightness.

Turning to the testing method, a hydrostatic pressure was applied at apressurizing rate of 0.3 kg/cm²/sec and the pressure on cleavage of themetal foil was measured.

The result was that the metal foil 2 was cleft beginning from thethin-walled portion 5 of the weld 9 formed at the time of cold welding.The measured results of the cleavage pressure indicated that thepressure values ranged from 15 to 20 kg/cm², which is satisfactory withrespect to the targeted value of 18 kg/cm².

This lid 1 was inserted into the opening of the cell can 3 and weldedthereto by light beam welding to complete a hermitically sealed vessel.

The lid 1 and the metal foil 2, cold pressure welded together, weresevered in a plane normal to the plane of the lid 1. While the weld 9and thin-walled portion 5 were checked as to plate thickness over amicroscope, the separation between the ends of the upper punch 6 and thelower punch 7 and other conditions were adjusted to search for the lowerlimit of the plate thickness of the thin-walled portion 5. It was foundthat lower range of the—therefor; plate thickness is about 0.005 mm.

Since it is possible with the present safety valve to produce thethin-walled portion 5 to a plate thickness of not more than one-halfthat achieved with the conventional technique, an appropriate cleavagepressure ranging from 15 to 20 kg/cm² is realized even if the valve isreduced in size for mounting in a small-sized cell vessel as in thepresent embodiment.

Referring to FIG. 6, the weld 9 of the metal foil 2 produced by the coldpressure welding was crushed under the pressure of the cold pressurewelding mold, with the produced pads then becoming concentrated towardsthe center to produce a dome 11.

If the pads were not formed into a dome, there were produced wrinkles inthe metal foil, thus producing the leakage at the folded portions orleading to an unstable cleavage pressure.

The dome 11 can be made convex on the inner side or on the outer side ofthe cell vessel by adjustment at the pressure welding mold. In the caseof the sample convexed on the inner side of the cell vessel, thecleavage pressure on pressure application from the inner side of thevessel was found to be 15 to 20 kg/cm², while that on pressureapplication from the outer side of the vessel was found to be 50 to 60kg/cm².

It was found that, if the dome 11 was convexed on the inner side of thevessel, the vessel was cleft at a moderate cleavage pressure against thepressure applied from inside of the vessel, while it exhibited pressureproofness on application of the pressure from outside which is more thandouble the pressure value applied from the inside. Thus, it was foundthat the inwardly convexed dome 11 gives more desirable properties ifthe present safety valve is used as a safety valve for the cell.

FIGS. 9 to 11 show the process up to cleavage of the dome 11.

In these figures, the lower side and the upper side with respect to thelid represent the inner and outer sides of the vessel, respectively.

FIG. 9 shows the normal state in which the internal pressure of thevessel is not up to the proscribed value, while FIGS. 10 and 11illustrate the state of dome rehearsal when the internal pressurereaches the prescribed value and the state of cleavage of thethin-walled portion 5 directly after the dome reversal leading toopening of the internal pressure.

It was also found with the present safety valve that the portion of theinner surface of the weld 9 surrounding the thin-walled portion 5performs the role equivalent to the pressure-receiving portion 10 of themarker type safety valve thus inducing cleavage of the thin-walledportion 5 to promote reliable cleavage at a moderate cleavage pressure.

Industrial Applicability

Since the present safety valve has characteristics of easily realizing amoderately low cleavage pressure, even if the valve is reduced in sizefor mounting on a small-sized vessel, it is cleft with high precisionwhen mounted as a safety valve in a metal vessel of, for example, ametal vessel, such as a high-performance secondary cell used in aportable equipment or the like, thus assuring safety of the user andpreventing destruction of the equipment.

From the above description, it is apparent that the objects of thepresent invention have been achieved. While only certain embodimentshave been set forth, alternative embodiments and various modificationswill be apparent from the above description to those skilled in the art.These and other alternatives are considered equivalents and within thespirit and scope of the present invention.

What is claimed is:
 1. A cleavage safety valve for a metal vessel, thevessel having, a plate thickness and including an air vent hole having adiameter, the valve comprising: a piece of metal foil comprising acental portion and an outer periphery that is connected to the vessel bycold welding, the metal foil further comprising a thin-walled portiondisposed radially inward from and adjacent to the outer periphery, thethin-walled portion being created by the cold welding of the outerperiphery of the metal foil to the vessel, the thin-walled portion beingfree of cracks and scores, the metal foil covering the air vent hole toprovide a hermetic seal over the hole, the central portion of the metalfoil having a plate thickness, the thin-walled portion of the metal foilhaving a plate thickness that is less than the plate thickness of thecentral portion, whereby an increased internal pressure inside the metalvessel above a predetermined value results in a cleavage of the metalfoil at said thin-walled portion.
 2. The valve of claim 1 wherein aratio of the plate thickness of the central portion of metal foil to theplate thickness of the vessel being about 3:80, and a ratio of the platethickness of the central portion of the metal foil to the diameter ofthe hole being about 3:150.
 3. The valve of claim 1 wherein the vesseland the metal foil are fabricated from A3003.
 4. The valve of claim 1wherein the vessel has the dimensions 34 mm×6 mm×47 mm and the platethickness of the vessel is about 0.8 mm and the plate thickness of thecentral portion of the metal foil is about 0.03 mm.
 5. A cleavage safetyvalve for a metal vessel, the vessel having a plate thickness of about0.8 mm and including an air vent hole having a diameter of about 1.5 mm,the valve comprising: a piece of metal foil comprising a central portionand an outer periphery, the outer periphery being connected to thevessel by cold welding, the metal foil further comprising a thin-walledportion disposed radially inward from and adjacent to the outerperiphery, the thin-walled portion being created by the cold welding ofthe outer periphery of the metal foil to the vessel, the thin-walledportion being free of cracks and scores, the metal foil covering the airvent hole to provide a hermetic seal over the hole, the central portionof the metal foil having a plate thickness of less than or equal to 0.03mm, the outer periphery of the metal foil having a plate thickness ofless than the plate thickness of the central portion of the metal foil.6. The valve of claim 5 wherein the vessel and foil are both fabricatedfrom A3003.
 7. The valve of claim 5 wherein the vessel has thedimensions 34 mm×6 mm×47 mm.
 8. A cleavage safety valve for a lid of ametal vessel, the lid having a plate thickness of about 0.8 mm andincluding an air vent hole having a diameter of about 1.5 mm, the valvecomprising: a piece of metal foil connected to the lid by cold pressurewelding and covering the air vent hole to provide a hermetic seal overthe hole, the metal foil having central portion with a plate thicknessof less than or equal to 0.03 mm and an outer periphery that is coldwelded to lid, the metal foil further comprising a thin-walled portiondisposed radially inward from and adjacent to the outer periphery, thethin-walled portion being created by the cold welding of the outerperiphery of the metal foil to the vessel, the thin-walled portion beingfree of cracks and scores, the thin-walled portion having a platethickness of less than the plate thickness of the central portion of themetal foil.
 9. The valve of claim 8 wherein the metal foil, lid andvessel are fabricated from A3003, the vessel has a plate thickness ofabout 0.8 mm, the lid is about 34 mm long and about 6 mm wide, thevessel is about 34 mm long, about 6 mm wide and about 47 mm deep.
 10. Acleavage safety valve for a lid of a metal vessel, the lid and vesselboth being fabricated from A3003 and both having a plate thickness ofabout 0.8 mm, the lid being about 34 mm long and about 6 mm wide, thevessel being about 34 mm long, about 6 mm wide and about 47 mm deep, thelid including an air vent hole having a diameter of about 1.5 mm, thevalve comprising: a piece of metal foil connected to the lid by coldwelding and covering the air vent hole to provide a hermetic seal overthe hole, the metal foil comprising A3003 and having a central portionwith a plate thickness of less than or equal to 0.03 mm and an outerperiphery that is connected to the lid, the outer periphery comprising athin-walled portion having a plate thickness of less than the platethickness of the central portion of the metal foil, the thin-walledportion being created by the cold welding of the outer periphery of themetal foil to the vessel, the thin-walled portion being free of cracksand scores.
 11. An enclosed vessel comprising: a vessel body with anopen end connected to a lid, the lid comprising an air vent hole, theair vent hole being hermetically sealed by a metal foil the forms acleavage safety valve, the metal foil having a plate thickness, themetal foil comprising a central portion and an outer periphery, themetal foil further comprising a thin-walled portion disposed radiallyinward from and adjacent to the outer periphery, the outer peripherybeing connected to the lid by cold welding that reduces plate thicknessof the metal foil at the outer periphery and at said thin-walled portionso that an increased internal pressure inside the metal vessel above apredetermined value results in a cleavage of the metal foil at saidthin-walled portion, the thin-walled portion being free of cracks andscores.
 12. The vessel of claim 11 wherein the lid, vessel body andmetal foil are fabricated from A3003, the lid and vessel body bothhaving a plate thickness of about 0.8 mm, the metal foil comprisingA3003, the cental portion of the metal foil having a plate thickness ofless than or equal to 0.03 mm.
 13. The vessel of claim 11 wherein thelid is about 34 mm long and about 6 mm wide, the vessel is about 34 mmlong, about 6 mm wide and about 47 mm deep.
 14. The vessel of claim 11wherein the vessel can withstand an internal pressure of at least 15kg/cm² prior to cleavage of the outer periphery of the metal foil. 15.The vessel of claim 11 wherein the vessel can withstand an externalpressure of at least 50 kg/cm² prior to cleavage of the outer peripheryof the metal foil.
 16. A method of forming a cleavage safety valve in avessel, the method comprising the following steps: providing a vesselbody, providing a lid for the vessel body, forming an air vent hole inthe lid, cold welding an outer periphery of a metal foil layer over theair vent hole to hermetically seal the air vent hole and creating athin-walled portion disposed radially inwardly of and adjacent to theouter periphery, the thin-walled portion being free of cracks andscores, welding the lid to the vessel body.
 17. The method of claim 16wherein the vessel, lid and foil all comprise A3003, the vessel and lideach having a plate thickness of about 0.8 mm, the foil layer having auniform plate thickness prior to said cold pressure welding step ofabout 0.03 mm, the plate thickness of the outer periphery and thethin-walled section of the foil layer after the cold welding beingsubstantially less than 0.03 mm.
 18. The method of claim 16 wherein thelid is about 34 mm long and about 6 mm wide, the vessel is about 34 mmlong, about 6 mm wide and about 47 mm deep.
 19. The method of claim 16wherein the plate thickness of the outer periphery of the foil layerafter the cold welding step ranges from less than 0.03 mm to about 0.005mm.